Regulated current power supply with isolated secondary and output current limiting

Abstract

A regulated power supply for application in a cable signal distribution amplifier comprises a filter, voltage doubler and current sense transformer controlled by a control technique known in the art. In the event of a high impedance short condition causing severe overcurrents, the known control technique is ineffective. To alleviate the problem, a high impedance current fault control circuit includes a sampling circuit, a level adjusting circuit, a differential amplifier for providing a monitor output control voltage and a buffer circuit to the controller. In the event of a high impedance current fault, the control circuit kicks in and interrupts controller operation saving power supply components from damage caused by the overcurrent condition.

What I claim is: 
     
       1. A regulated power supply comprising a filter, voltage doubler and current sensing transformer, the power supply regulated by a controller, the improvement comprising: a sampling circuit for sensing an output over current condition via a monitored voltage drop, wherein the sampling circuit comprises a resistor having first and second terminals;   a level adjusting circuit coupled to the sampling circuit for adjusting the level of the monitored voltage drop, the level adjusting circuit comprising a first input coupled to the first terminal of the resistor of the sampling circuit; a second input coupled to the second terminal of the resistor of the sampling circuit; a first processing circuit coupled to the first input for generating a first output; the first processing circuit comprises first and second diode connected transistors; and a second processing circuit coupled to the second input for generating a second output;   a differential amplifier, coupled to outputs of the level adjusting circuit, for providing a monitor output voltage, wherein the differential amplifier comprises a first input coupled to the first output of the level adjusting circuit, a second input coupled to the second output of the level adjusting circuit; and an output for providing the monitor output voltage; and   a buffer circuit connected to the output of the differential amplifier for interrupting controller operation to thereby interrupt current flow at an output of the regulated power supply.   
     
     
       2. The regulated power supply of claim 1, wherein the first and second diode connected transistors have similar turn-on voltages and drifts over temperature. 
     
     
       3. The regulated power supply of claim 2, wherein the first and second diode connected transistors are manufactured from the same silicon die. 
     
     
       4. The regulated power supply of claim 1, wherein the second processing circuit comprises: third and fourth diode connected transistors.   
     
     
       5. The regulated power supply of claim 4, wherein the third and fourth diode connected transistors have similar turn-on voltages and drifts over temperature. 
     
     
       6. The regulated power supply of claim 5, wherein the third and fourth diode connected transistors are manufactured from the same silicon die.